The link is formed by the the Respiratory Rhythmicity Centre.
The Respiratory Rhythmicity Centre consists of groups of nerves in the medulla of the brain that control the rate and depth of each breath.
Motor impulses are sent from the respiratory centre along the spinal cord and on to the intercostal muscles via the intercostal nerves and on to the diaphragm via the phrenic nerves.
Receptors called chemoreceptors, located on the surface of the medulla, respond to changes in the pressure levels of oxygen and carbon dioxide in the blood and cerebrospinal fluid. If change is detected, the chemoreceptors stimulate the respiratory system and breathing rate and depth are increased. An example of this is cardiovascular exercise.
When exercising, the muscles demand more oxygen.
Respiratory rate and depth increase to deal with this demand.
As a result the muscles generate greater amounts of C02, which stimulate the chemoreceptors.
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